This invention relates to the art of fields necessary for controlling light through convergence, diffusion, reflection, diffraction and the like, e.g. the art of fields such as of display, illumination, medical treatment, optical communication, computers and the like, which require microlenses. More specifically, the invention relates to a microlens array employed for the manufacture of a reflection-type liquid crystal display device and a diffuse reflector plate of a solar cell requiring a high efficiency, a method for making a transfer master pattern for a microlens array, a concave and convex pattern obtained from the transfer master pattern, a laminate for transfer, and a liquid crystal display device.
A microlens array has been used for forming a diffraction grating filter, optical parts for optical communication or a focussing glass of camera parts. The microlens array takes a round or circular form having a diameter of approximately 10 to 30 xcexcm with a depth of 0.6 to 50 xcexcm. Usually, the microlens array is designed in a spherical form which is axially symmetrical with respect to the center thereof. For the measure of manufacturing a microlens, an indentation system set out in Japanese Unexamined Patent Publication Nos. Hei 9-327860 and Hei 11-42649 and a photolithographic system (hereinafter referred to merely as photolitho system) as proposed in Japanese Unexamined Patent Publication No. Hei 6-194502 wherein etching is performed after exposure to light are known. A fly cutting system, in which a lens face is rotationally cut while rotating a cutting tool, is known.
An instance of a lens array where microlenses are arranged at equal pitches includes a diffraction grating filter used as an optical part or an optical communication part. On the other hand, an instance of a microlens array of the type wherein microlenses are arranged at uneven pitches includes a reflector plate for preventing iridescent reflection and reflecting white light or a reflection electrode member for a reflection-type liquid crystal. For this purpose, it is necessary that several millions to several tens of millions of microlenses be formed.
For the processing of spherically designed microlenses, such microlenses are frequently formed according to the photolitho method. As a measure of mechanically controlling the processing dimension of a microlens, an indentation technique and a fly cutting technique using rotary cutting are used, respectively.
A liquid crystal display (hereinafter abbreviated as LCD) makes use of such features as to be thin, small in size and low in consumption power and has now been in use as a display unit of watches, desk-top calculators, TV sets, personal computers and the like. Further, in recent years, color LCD has been developed and started to be employed in various fields including, aside from those of OA devices and AV devices, those of navigation systems, view finders, monitors of personal computers and the like. Thus, it has been expected that its market will be drastically extended. Especially, attention has been paid to reflection-type LCD, in which light incident from outside is reflected for display, for application to a portable end instrument from the standpoint that back light is unnecessary with small consumption power, and thus, thinning and weight saving are enabled. For conventional reflection-type LCD, a twisted nematic system and a super twisted nematic system have been adopted. These systems become dark in display because xc2xd of incident light is not utilized for the display by the influence of linear polarizers. To avoid this, the display mode of a system wherein the polarizer is reduced to one in number and is combined with a phase plate or a phase transfer guest or host system has been proposed.
In order to obtain a bright display by efficiently utilizing external light in reflection-type LCD, it is necessary that the intensity of light scattered in directions vertical to a display face be increased with respect to incident light from all angles. To this end, a reflection film on a reflector plate should be so controlled as to impart appropriate reflection characteristics thereto.
A method of forming a diffuse reflector plate has been proposed in Japanese Unexamined Patent Publication No. Hei 4-243226, in which a photosensitive resin is coated onto a substrate and patterned by use of a photomask to form fine irregularities, each with a size of several micrometers, and a metal thin film is formed thereon.
Further, Japanese Unexamined Patent Publication No. Hei 11-42649 proposes a method of making a transfer master pattern wherein an indentater having a spherical tip is pressed thereby continuously forming concave configurations and also a method of making a reflector plate by transferring the pattern to a reflector substrate.
Moreover, a method of forming, on a substrate, a film made of fine particles dispersed in a resin so as to control diffusability in Japanese Unexamined Patent Publication No. Hei 7-110476.
Where a microlens array is formed according to a photolitho method, this process is carried out through chemical reaction, making it difficult to control the shape or configuration of individual microlens faces. Especially, in a reflector plate of the type wherein microlenses are arranged at irregular or uneven pitches, the sizes of adjacent microlenses differ from each other with a problem on the control of depth, so that the control of the configuration becomes difficult. As a result, the arrangement of axially symmetric spheres is difficult.
FIG. 20 is a perspective view of an indentation tool and an indentation master block showing a method of forming microlenses by an indentation system. In order that an axially symmetric spherical configuration is formed in the indentation system shown in the figure, it is necessary to avail a tool having a spherical form. For the tool, a diamond indentater 60 is usually employed. If the diamond indentater 60 can be constituted of a single crystal, a tool having a completely spherical face can be obtained. Diamond has a harder face and a softer face depending on the crystal orientation, so that it is difficult to finish the tool as having a complete sphere. Strictly speaking, the configuration of the tool has anisotropy. Especially, if an aspheric surface configuration in an axially symmetric form is desired, it is very difficult to obtain an intended configuration profile. In this sense, a difficulty is involved in forming a microlens 62 of a desired configuration in an indentation matrix 63 by means of the diamond indentater 60. Although such a tool is available when using a super hard material with which an intended tool shape is liable to obtain, the tool made of a polycrystal material is disadvantageous in that not only the surface roughness at the tip thereof becomes poor, but also durability is not good when a great number of indentations are formed. Moreover, the indentation method has the problem that with the irregular pitches ascribed to the plastic flow of material, the configurations differ depending on the density of the irregular pitches.
With the fly cutting using rotary cutting, the profile accuracy of a tool is two-dimensionally controlled, making it possible to process the tool as having a configuration of high accuracy. In order to obtain an axially symmetric microlens, it is necessary to set the radius of cutting edge of a tool and the position of a rotation center in high accuracy, under which where the diameter of a microlens is at about 10 xcexcm or below, it is very difficult to determine the center of rotation. In addition, the axially symmetric configuration of an aspheric face is difficult to process.
In the method set forth in Japanese Unexamined Patent Publication No. Hei 4-243226, the formation of concave and convex configurations includes the steps of exposing every substrate to light through a photomask and developing, so that the procedure is complicated, and thus, is neither low in cost or high in productivity. Additionally, the random formation of patterns over a large area is difficult in the step of making a photomask.
In the method of Japanese Unexamined Patent Publication No. Hei 11-42649, a concave configuration with several microns in size is formed one by one by impressing a fine indentater, thus involving a difficulty in processing over a large area.
In Japanese Unexamined Patent Publication No. Hei 11-38214, a method is proposed, in which granules are jetted against striped grooves to randomly make concave portions. However, it is difficult to obtain a satisfactory processing accuracy.
In the method of Japanese Unexamined Patent Publication No. Hei 7-110476, some problems are found in that a difficulty is involved in uniform dispersion of fine particles, and a reflection intensity within a necessary range is obtained only when reflection at a direct reflection angle increases, thus causing the occurrence of a light source being reflected.
An object of the invention is to solve the drawbacks of the above-stated prior art and to provide a technique of manufacturing a microlens array in an axially symmetric spheric or aspheric surface, a microlens array having excellent reflection characteristics, a transfer master pattern and a concave and convex pattern employed for the manufacture of a diffuse reflector plate such as reflection-type LCD having good reflection characteristics, methods for making these patterns, a laminate for transfer using same, a diffuse reflector plate, and a reflection-type liquid crystal device using the reflector plate.
In order to achieve the object of the invention, a microlens array is provided, according to a first embodiment of the invention, which comprises microlenses, each arranged such that a major axis and a minor axis thereof, which pass through a center of a substantially circular profile and intersect at 90 degrees, are substantially equal in length to each other, and sectional forms at faces vertical to an axis parallel to the major axis or the minor axis, respectively, have the same curved shape at any position.
According to a second embodiment of the invention, a microlens array is provided, which comprises microlenses, each having a profile of a substantially circular form and arranged such that a major axis and a minor axis thereof, which pass through a center of the substantially circular form and intersect at 90 degrees, are equal in length to each other, and sectional forms at faces vertical to an axis parallel to the minor axis or the major axis, respectively, have a size of radius at any position.
According to a third embodiment of the invention, a microlens array is provided, which comprises microlenses, each having a profile of a substantially circular form and arranged such that a major axis and a minor axis thereof, which pass through a center of the substantially circular form and intersect at 90 degrees, are equal in length to each other, and sectional forms at faces vertical to an axis parallel to the minor axis or the major axis, respectively, have a given aspheric form.
According to a fourth embodiment of the invention, a microlens array is provided, which comprises microlenses, each arranged such that in a major axis and a minor axis thereof intersecting at 90 degrees, sectional forms at faces vertical to the major axis or minor axis, respectively, have the same curve or the same form of a combination of a curved line and a straight line in the respective directions at any position.
According to a fifth embodiment of the invention as set forth in the first to third embodiments, a curved face constituting the microlens surface at a horizontal face of a transfer master pattern forming the microlenses has a tangential angle of 23 degrees or below.
According to a sixth embodiment of the invention, a method for making a microlens transfer master pattern is provided, which comprises forming a microlens configuration in a substrate by controlling a cutting tool having the same nose or edge profile as a shape in section or sectional form of one of a minor axis and a major axis of a microlens so that the cutting tool draws a locus of a sectional form of the other axis.
According to a seventh embodiment of the invention, a method for making a transfer master pattern for a microlens array is provided, which comprises the steps of forming a nose profile of a diamond tip serving as a cutting tool in the same sectional form as one of a major axis or a minor axis of a microlens, and processing a substrate by controlling a locus of the cutting tool so as to make the same sectional form of the other axis of the microlens, thereby forming a microlens configuration.
In an eighth embodiment of the invention as set forth in the sixth or seventh embodiment, the microlens is shaped substantially in a circular form wherein when a diameter of the circle is taken as D and a radius of the nose profile is taken as R, D/R is 0.73 or below.
In a ninth embodiment of the invention as set forth in the sixth or seventh embodiment, the microlens is formed by moving one of the cutting tool or the substrate in a horizontal direction and moving a drive mechanism for fine movement in vertical directions.
In a tenth embodiment of the invention as set forth in the ninth embodiment, the drive mechanism for fine movement is made of an piezoelectric element, and the microlens is formed by applying a voltage to the piezoelectric element and moving the cutting tool in vertical directions by a very small degree.
In an eleventh embodiment of the invention, a transfer master pattern of a reflector plate member comprises microlenses, each having a profile of a substantially circular form wherein a major axis and a minor axis thereof pass through a center of the substantially circular form and intersect at 90 degrees are substantially equal in length to each other and sectional forms of faces vertical to an axis parallel to the major axis or the minor axis are in the same curved shape at any position, the microlenses being formed at irregular pitches on a plane and a pitch between adjacent microlenses is within a range of 50 to 100% of a radius of the microlenses.
In a twelfth embodiment of the invention, a transfer master pattern of a reflector plate member comprises microlenses, each having a major axis and a minor axis thereof which intersect at 90 degrees and in which sectional forms of faces vertical to the major axis or the minor axis are in the same curved line or in the same form of a combination of a curved line and a straight line in the respective directions at any position, the microlenses being formed at irregular pitches on a plane and a pitch between adjacent microlenses is within a range of 50 to 100% of a width of the microlenses.
In a thirteenth embodiment as set forth in the sixth, seventh or eighth embodiment, a method for making a transfer master pattern of a reflector plate member is provided, which comprises forming, at irregular pitches on a plane, microlenses each having a profile of a substantially circular form wherein a major axis and a minor axis thereof that pass through a center of the circular form and intersect at 90 degrees are substantially equal in length to each other and sectional forms of faces vertical to an axis parallel to the minor axis or the major axis are in the same curved line at any position, and setting a pitch between adjacent microlenses within a range of 50 to 100% of a radius of the microlenses.
In a fourth embodiment of the invention as set forth in the sixth or seventh embodiment, a method for making a transfer master pattern of a reflector plate member is provided, which comprises forming, at irregular pitches on a plane, microlenses whose major axis and minor axis intersect at 90 degrees, in such a way that sectional forms of faces vertical to the major axis or the minor axis are in the same curved line or in the same form of a combination of a curved line and a straight line in the respective directions at any position, and setting a pitch between adjacent microlenses within a range of 50 to 100% of a width of the microlenses.
In a fifteenth embodiment of the invention, a method for making a concave and convex pattern is provided wherein the transfer master pattern set forth in the eleventh to fourteenth embodiments is provided and a substrate to be transferred is held against the transfer master pattern to form a concave and convex pattern.
In a sixteenth embodiment of the invention as set forth in the fifteenth embodiment, the substrate to be transferred is made of a laminate including a plastic film or an underlying layer. The plastic film or underlying layer is not critical with respect to the type of material so far as it ensures faithful reproduction of a transfer master pattern with respect to the transfer configuration and high stability in configuration.
In a seventeenth embodiment of the invention, the concave and convex pattern is made according to the method set forth in the fifteenth or sixteenth embodiment.
In an eighteenth embodiment of the invention, a laminate for transfer is formed by providing the concave and convex pattern set forth in the seventeenth embodiment as a provisional support, and laminating a thin film layer on the concave or convex microlens configuration pattern surface of the provisional support so that a surface of the thin film layer opposite to a surface in contact with the provisional support serves as a bonding face to an application substrate.
In a nineteenth embodiment as set forth in the eighteenth embodiment, a protective film is further laminated on the bonding face of the thin film layer.
In accordance with a twentieth embodiment of the invention, a method for making a diffuse reflector plate is provided, which comprises the steps of holding the transfer laminate set forth in the nineteenth embodiment, from which the protective film has been removed, against the application substrate in such a way that the bonding face of the thin film layer is in contact with the substrate, separating the provisional support, and forming a reflective film on concave and convex pattern surface of the thin film layer.
In a twenty and first embodiment of the invention, a method for making a diffuse reflector plate, which comprises the steps of holding the concave and convex pattern set forth in the seventeenth embodiment against a thin film layer formed on a protective substrate so that the concave and convex pattern surface is in contact therewith, separating the concave and convex pattern, and forming a reflective film on a surface on which the concave and convex pattern surface of the thin film layer is transferred.
In a twenty and second embodiment, a reflective film is laminated on the concave and convex surfaces of the concave and convex pattern set forth in the fifteenth embodiment.
In a twenty and third embodiment, a liquid crystal display device is provided, which comprises the diffuse reflector plate manufactured according to the method for making a diffuse reflector plate as set forth in the eighteenth or nineteenth embodiment.
In the practice of the invention, the microlens can be processed by cutting with use of a diamond bite, and the profile control of a cutting tool is based on the two-dimensional profile pattern control of a cutting edge, so that a tool of high precision can be obtained. This tool is used and controlled with respect to a desired sectional form or an R face relative to a member to be processed, under which the processing is performed such that the direction of cutting is coincident with a direction extending along one of the axes passing through the center of microlens and intersecting at 90 degrees. In this way, the sectional form relative to the central line parallel to the cutting direction results in the same form as the tool profile. With respect to the sectional form relative to a central line along a direction at right angles to the cutting direction, the dimension obtained is based on the control of movement of the tool. In both cases, the dimension can be mechanically controlled, so that a microlens configuration pattern of high precision can be formed. Hence, when using the microlenses obtained according to the method of the invention without resorting to the technique of axially symmetric formation, a lens array of high precision can be formed.
Further, where the microlens configuration pattern of the invention is used as a transfer master pattern of a reflection member for transfer shaping, a great number of microlens configurations are contiguously formed in the surface of a substrate for the transfer master pattern. In this case, the resultant concave microlens configurations should preferably be arranged randomly rather than regularly.
The configuration of the transfer master pattern is reversely transferred to a material to be transferred such as a film or the like thereby providing a concave or convex microlens configuration pattern such as a concave and convex pattern-bearing film or the like. This is provided as a provisional support and a thin film layer is laminated on the concave and convex surfaces to obtain a laminate for transfer. The laminate is brought into contact with an application substrate (perpetual substrate) made of a glass substrate or the like in such a way that the surface of the thin film layer that is not in contact with the provisional support is held against the perpetual substrate, followed by separating the provisional support and forming a reflective film on the thin film layer. As a result, a diffuse reflector plate can be manufactured at high productivity and a large-sized diffuse reflector plate can be efficiently produced. A substrate for master pattern (which may be used as a transfer master pattern) wherein a great number of microlens configurations have been contiguously formed is used to make a reverse transfer pattern based thereon, and a plurality of the reverse transfer patterns are connected with one another and provided as a master pattern to make a further reverse transfer master pattern. When the last-mentioned master pattern is used, a large-sized diffuse reflector plate can be manufactured at higher productivity.
Alternatively, the diffuse reflector plate may be manufactured by forming a reflective film on the concave or convex surfaces of the concave and convex pattern used as a provisional support, laminating a thin film layer thereon to provide a laminate for transfer, bringing a surface of the thin film layer, which is opposite to the surface in contact with the provisional support, into contact with the perpetual substrate to hold the film against the substrate, and separating the provisional support.
Still alternatively, the diffuse reflector plate having excellent reflection characteristics may be likewise manufactured by transferring the concave or convex surfaces of the concave and convex pattern to the thin film layer preliminarily formed on the perpetual substrate while bringing the concave or convex surfaces into contact with the thin film layer to hold the surfaces against the layer, and forming a reflective film on the thin film layer.
Because the individual concave and convex configurations of the transfer master pattern are so controlled as to reduce reflection at a direct reflection angle, the reflection of a light source per se is lessened, so that a diffuse reflector plate having a uniform reflection intensity over a necessary range can be readily manufactured.
The diffuse reflector plate of the invention has concave and convex configurations with good diffuse reflection characteristics formed in high reproducibility and can be manufactured by a simple procedure.
This and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.